Biometrics that is used to authenticate and identify personal information is usually realized through physical characteristics (e.g., hair, fingerprints, blood, etc.). When choosing physical characteristics, considerations are given to different aspects, such as the cost of production, ease of processing, reliability, comfort, and so on. Fingerprint is the most reliable feature in biometrics. It is uniquely special, yet in the personal consumer market, application of fingerprints is not very mature because it is affected by production design on the one hand, and restricted by cost factors on the other hand.
So far the principle employed by the fingerprint sensor device mainly involves optics, integrated pressure, capacitance, and the like. The main reason for the disadvantage of the optical imaging fingerprint identification unit is that it creates a relatively large volume and requires a clean surface; the major restriction for integrated pressure sensing unit is the supper high cost because it is not commonly used; and fingerprint information detection circuit based on capacitive sensing unit may avoid the disadvantages of the first two methods, with its general circuit configuration shown in FIG. 1, comprising a signal input unit, a reset unit, an amplification unit, a feedback unit and a source follower unit.
In FIG. 1, 101 is a signal input unit, 102 is a reset unit, 103 the amplification unit, 104 the feedback unit and 105 the source follower unit.
However, the above-described circuit takes up a huge chip area, increasing the cost on chips.
In addition, the clock feedthrough effect and the electric charge injection effect generated by the reset unit affect the voltage signal outputted by the circuit, namely affecting the results of fingerprint detection.